i think you are misrepresenting a given fact while unibody suv's have more crumple zones this only helps the other veh inwhich you are involved with. as the crumple zones absorbe more energy. however framed suv's survive much better than the rest and i think that is something alot of people are looking at when it comes to safety.

Well yes the framed vehicles themselves survive better, however I'm pretty sure that the impact is transfered to the occupants more in framed vehicles than non-framed as a general rule of thumb. With large trucks however there are still crumple zones and thus still safe.

Interesting thing happened over the weekend at a road race my team was involved in. Our car weighs 3100lbs and a competitor driving a 1700lb car tried to knock us off the road course in a turn, unfortunately for him he bounced off our car and spun off the track, we continued on w/o issue. So weight does play a factor.

I also don't see the frame on SUV going away, they are quite useful in towing and hauling applications.

A BOF vehicle is more rigid than a unibody vehicle. In the parlance of the "crash research" community, a BOF vehicle is stiffer. A unibody vehicle has a deeper and more controlled crumple zone and gives more in a crash. If the intergity of the passenger compartment is not compromised, a unibody vehicle protects its occupants better than a BOF because the unibody vehicle spreads out the crash forces in time and reduces the peak crash accelerations experienced by the occupants.

But here's what is not sometimes understood: the less stiff vehicle protects both its own occupants and the occupants of any vehicle it crashes into.

In a head-on crash between a BOF and a unibody, the crumple zone in the unibody reduces the peak crash forces experienced by the occupants of both vehicles. This is the case because in a two-vehicle crash the vehicles exert equal but opposite forces on each other. This is one of Newton's laws relating force and motion.

The forces are always equal in magnitude, but if one of the vehicles is more massive than the other, the effect of the forces on the vehicles will be different. Remember that F = m a, so a = F/m. That is, the crash acceleration of the lighter vehicle will be greater than that of the heavier vehicle because the F is the same for both vehicles, but m is different, and this is in the denominator.

The injury to the occupants of a vehicle is strongly related to the peak crash acceleration that the vehicle experiences.

Consider a head-on crash between two Suburbans, identical except that one is red and one blue. Each is travelling at 30 mph relative to the ground. High and identical peak crash forces are transmitted to the occupants of the two vehicles

Now consider the same crash except that a serious but lightweight engineered crush zone 4 ft in depth has been attached to the front of the red Suburban. That is, the two Sururbans are still the same mass. The result will be lower peak crash accelerations to both vehicles.

The crumple zone strapped to the red Suburban has protected equal benefit to the occupants of the blue one.

If both vehicles had had the same 4-ft crumple zone, then the peak crash accelerations would be even less because there would be a total of 8-ft of crumple zone. If each vehicle had had the same design 2-ft crumple zone it would be the same as either one having a 4-ft crumple zone.

BOF and crumple zone are not mutually exclusive. Framed vehicles can have crumple zone built in them as well. In fact, the concept of the crumple zone is often combined with providing a more rigid structure encompassing the passenger space. Mercedes has been using crumple zone technology since the late '50s.

Within the limits of what people can afford, every attempt should be made, and presumably is made by the manufacturers, to make the passenger compartment as rigid as possible. You don't want the passenger compartment to deform, nor do you want anthing to "intrude" into the passenger compartment. Clearly intrusions are potentially extremely injurious. It seems to me that both BOF and unibody designs could have equally rigid and strong passenger compartments.

But it also seems to me that a unibody would be less stiff than a BOF design outside the passenger compartment and so would protect from the other source of crash injury to vehicle occupants--the high peak g-forces of the passenger compartment due to the sudden change in velocity (the "delta-V") that occurs in a collision.

I personally am attracted to the idea of a body-on-frame design because I drive conservatively and I "don't think" I'll be in a crash. I am sure that I must underestimate my risk. I value strength and durability in a vehicle. At my age, early 60s, I enjoy imagining that the car I'm driving (2004 base V70) will be the last car I'll buy.

My ideal vehicle would be a BOF "minivanoid" with relatively high seating position (comfortable leg angle), 3000-lb curb weight, powered by a small gas or diesel engine (120 hp max) and a 6-spd manual. It would be rated to tow up to 2000 lb. It would have a variable height suspension to get best fuel economy on pavement, but be able to go on rough roads when necessary.

But when I awaken from my dreaming I find that in the real world a unibody design will best protect me from crash injury at a price I can afford.

>> But it also seems to me that a unibody would be less stiff than a BOF design outside the passenger compartment

Less stiff does not necessarily translate into better crumple zones. On BOF vehicles, crumple zones are strategically placed in front and rear portion of the frame (often appear as tiny waves), so that when enough force is applied (i.e., when vehicle is hit hard), the frame will bend at certain points, and in certain directions. In other words, the way it "crumples" is controlled, and not by relying on the random way the metal may fold.

I'm hearing a lot of misunderstanding on this forum. Maybe some actual crash pictures of a BOF will help, compared to a unibody crash.

First, note how in these pictures BOF Example -- click on this..., the frame is low, and is still extending out, and has actually penetrated the barrier, representing another car. This is because the frame, with engine/suspension mounts is very stiff and tough, and will skewer the occupants of other, lower vehicles if the BOF hits on a door. Very dangerous. What Ford has done on the above late-model F-150 is to secure the cab to the very tough frame to keep it from collapsing, although the protruding frame doesn't make a great "crumple" zone at all.

Now compare that to Unit body crash click here... where the front end is much flatter, with no protruding tough frame to stick out and through the barrier.

Conclusions: The frames on pickup trucks and SUVs protrude and can enter a unibody structure. The frames are very stiff and don't collapse much when hitting a unibody vehicle.

MY wife and i were in a 6 car pile up about 2 years ago, our doge was in the front and only took the rear bumper out the chevy taho be hind us and ours were the only ones to drive away and the only ones not having to go to hospital, the other 4 were totaled, we heat with wood and haul it in the durango we camp, and haul frinds around in car pool would not change even if some one gave me something els for free!!

Thats not a prob. in this area, i am a shade tree mec. but have rebuilt motors trans. and body work! i have about 30 junk yards that are in driving distance and i take good care of what i have. I do plan on gettin some donors so i have parts . the thing about me being in the front i had to keep my doge out of the back of a jag.

The most important safety feature on any vehicle is the driver. The most important thing in a two car accident is the weight of the vehicle. Heavy = Good! After that comes safety features such as airbags, anti-lock brakes etc. Please do not be fooled into thinking a five star front crash rating for a Honda Civic is the same as a five star front crash rating for a Ford Expedition. The Expedition weighs more than twice as much as the Civic and in a head on collision between the two, the person in the Civic is approximately 10 times more likely to die than the person in the Expedition. Oh yes, I know... Some bright person with an econo-box will be quick to jump in and say that an SUV is more likely to roll over than a Honda Civic. Yes this is true. According to government tests, the Civic has a 10% chance of a rollover and an Expedition has a 19%-21% chance of rollover depending on whether it is a 2wd or a 4wd. When was the last time you saw a rollover accident? I live in a huge metroplex and the last time I saw a rollover accident was about two years ago. The average accident that I see everyday is someone running into the back of someone, someone running a light etc. I realize my vehicle (Expedition in case you haven't figured that out yet) has a higher center of gravity but guess what? I drive with that in mind. It's not a sports car and I don't drive it like one. They even have decals on the driver's sun visor warning you that the vehicle has a higher center of gravity. Duh! When shopping for a vehicle, I want the heaviest full frame vehicle I can buy with the most safety features I can get. I weighed my Expedition (2008, 2wd, standard length) when I first got it. The vehicle with a full tank of gas in it, me and no gear scaled at 6,000 pounds. Now I could have got a Ford F-350 pickup that weighs between 7500 and 8500 pounds depending on how you get it equipped but I don't even think you can get side air-bags on one of those. The Expedition has front air-bags, side air-bags, canopy airbags and a host of other safety features because Ford considers it a family vehicle. Do I really need an eight passenger vehicle? Heck no! I'm single with no kids unless you count the dog. She enjoys having her own seat and her own air-conditioner. Sometimes I have me, the dog and the girlfriend in there and let me tell you there is plenty of room. Now on to crumple zones. It is easier to control the rate of crumple zone deformation in a unibody vehicle than a BOF. Now I appreciate the fact that when I hit a unibody car that it is going to soften the blow to me but the Expedition has pre-stressed points or dimples in the forward portion of the frame to buckle/deform at a controlled rate under an extreme impact. There is also about eight feet of crumple zone between me and the front of the Expedition. I don't worry about low speed impacts as much as I do high speed impacts or impacts with heavier vehicles. I am fully aware that if a 70,000 pound semi hits my Expedition, the airbags will do nothing more than provide me with a cushy, comfortable death. At the same rate though I am not going to put myself in something that weighs 2,700 pounds just to save a few dollars in gas. My Expedition when driven very easy gets 14-15 mpg in the city and up to 26 mpg on the freeway at 55 mph. At 12,000 miles a year, a Civic should burn about half as much fuel as the Expedition, which is roughly $700 for the Civic and $1,400 for the Expedition at current gas prices. That means an extra $58 a month it cost me in gas. But wait, what about the environment? Doesn't that big ol' 300 horsepower V8 engine put out more emissions? Probably so but one of my favorite meals is a heapin', hot bowl of spotted-owl soup (YUM YUM!) so that's not a big concern to me. Cars burn so cleanly these days that I really consider this to be a non-issue. I appreciate all of you people out there saving gas in your 30 mpg cars, that will increase my survivability rate in an accident and insure an ample supply of fuel for my vehicle for years to come. I wouldn't worry about the safety aspect of your econo-box though. As long as you don't collide with anything bigger than a butterfly, you'll probably be alright. Well that's about all I have for now. I have some spotted-owl burgers cooking on the grill and it's time to go flip them over. Happy motoring!

By your logic everyone would be driving big rigs...then your SUV would seem small! Luckily everyone is not selfish and actually thinks more about then just what they see in the mirror. Of cource that's one of the good reasons we have a government...to protect against selfish people who only think of themselves...happy motoring

We are suppose to give up our safety because you choose to purchase something that is inferior in an accident. My wife was in a 72 car pile up during a winter in Michigan and I'm very glad she was driving a Cheverlot Full size truck. Nobody in her vehicle was injured. I cannot say the same for the people who chose less safe vehicles. Agaiin a choice we make.

I would not be real quick to let our government decide what we drive. You may not like what they decide to regulate next.

It's not logic, just simple physics. The following quote is taken from the government document document

"Consider Vehicle WeightAll other things being equal, a heavier vehicle will generally better protect you in a crash. This is particularly the case in two-vehicle crashes. NHTSA research historically has shown that occupants in passenger cars are at a greater risk of being fatally injured when struck in the front or the side by a heavier and higher-riding light truck (such as a pickup) or SUV. Improved energy-absorbing front ends and safety technologies such as head-protecting side-impact air bags can help lower this risk to vehicle occupants."

I had also read somewhere that if a 6,000 pound vehicle has a head on collision with a 3,000 pound vehicle, the people in the lighter vehicle are eight times more likely to die than the people in the heavier vehicle. This seems to be inline with the government quote above.

One more thing Bob. Not that it matters even one iota but I work for the government and I'm quoting data collected by the federal government on their public website. Using their website www.safercar.gov was one of the main tools I used in my decision making process to purchase my Ford Expedition. I don't consider buying an Expedition "selfish" but if that's what you choose to believe go right ahead. You might also want to educate yourself on the subject at hand before you start hurling insults at someone. The free government publication I mentioned at the start of the post might be a good place for you to start.

Steve,

Yes the pickup trucks have a real frame and GM has been using hydro-formed rails on their trucks for sometime. Although I'm not an expert on hydro-formed rails I believe some of the advantages the hydro-formed rails have over a standard solid frame are increased strength, lighter weight and fewer welds.

I had read that GM is closing one of their pickup truck plants because of over capacity. By that I mean that they have the ability to build more pickups than they need and/or are selling. Pickups are definitely a big part of GM sales just like the F-150 is a big part of Ford's bottom line. What GM is going through now is bad for everyone and will just push unemployment higher. I wish them all the best.

TClark,

Glad your wife was not killed. Being in that truck that day probably saved her life or at the very least prevented a serious injury.

Of course being in a bigger car than you need might kill someone else in an accident unnecessarily.

For example, I would not like to be in a giant SUV involved in an accident with a smaller vehicle where some kids n the smaller vehicle was killed partly due to the fact that I was driving a vehicle much larger than I needed instead of something more reasonable that would not have caused some kids to get killed in the smaller car. But that's just me.

Or in the 72 car pileup example, while the folks in the big SUVs may have been less injured (although I don't see any facts indicating that was the case in this example) they probably did cause more injuries to others due to their vehicles having more weight and probably not able to stop as quickly. If everyone in that 72 car pileup was driving mid-sized sedans and no-one was driving trucks or giant SUVs, then maybe the overall number of injuries would have been less. Again, some people look at the needs of themselves only while others look at society in a number of issues.

I don't dispute the fact that in small vs large car collissions the large car will sustain less damage. I just think for society as a whole, the way to make the most drivers safe is to reduce the number of large vehicles on the road and not the other way around. And based on car sales, it looks like society is heading that way boosted by the price of gas and the price of cars...all a good thing.

"I would not be real quick to let our government decide what we drive. You may not like what they decide to regulate next. "Totally off subject, but I think many folks in America are paranoid of regulations, while the lack of regulations is a major cause of the problems in the economy or the lack of gun control is what causes violence to result in deaths versus injuries (eg...a kid goes wacko with a gun is going to cause a lot more deaths than if he's goes wack with a knife). And on the other hand land use regulations are what allow you to live in single family developments instead of having a polluting factory next door to you. Or look at photos of LA or any big city in the 1970s as compared to today and you'll see the benefit of regulations pretty clearly.

I haven’t done any actual research on breaking distance differences between SUVs and small sedans. I suspect that the difference in braking distance is probably less than 5%. Considering the difference in weight, my SUV is much more efficient in braking than a smaller sedan like a Honda Accord/Civic or something similar. I have seen the rotors (braking surface) on a Honda Civic and they are about the size of a coffee saucer. The rotors on my Expedition are massive and closer in size to a large dinner plate. Ford knows that I might want to pack a half dozen people in my SUV, load it up with camping gear, a 9,000 pound boat and drive up and down the Rocky Mountains. Trust me when I say that the brakes on my SUV are massively oversized/over designed and are less prone to overheating/fading/failure than those on small front wheel drive cars. Speaking of front wheel drive, that’s another reason I like my Expedition. Rear wheel drive is far superior to front wheel drive. Ever wonder why the most expensive cars in the world use rear wheel drive and the cheapest ones use front wheel drive? It all boils down to this. If someone wants to buy an 8,500 pound F-350 pickup to drive and someone else wants to ride around in a 2,500 pound Honda Civic, that’s their choice. Personally I choose to allocate more of my financial resources to the cost of driving a larger, safer vehicle because safety is of paramount concern to me. Freedom of choice is what makes America the greatest country in the world! Everyone should keep one thing in mind when operating an automobile, it’s not a matter of if you will be in an automobile accident, but when. Choose wisely grsshoppers.

The reviews I've read indicate that braking on Expeditions are spongy as compared to other similarly sized SUVs. "Trust me when I say that the brakes on my SUV are massively oversized/over designed" are you an engineer for the government?Rollover rating on the Expedition is pretty poor too.You can avoid an accident with a smaller and more nimble vehicle.Luckily large body on frame SUVs are selling less every year, so you're right Americans are making their choices, and more smartly now too for everyone.

Plus at least if you're going to spend the $$$ on an Expedition, do everyone else a favor and take a professional drivers course to keep those around you safe...happy driving and keep a safe distance in front of you and keep off the cell phone too. People driving huge SUVs are sort of like those legally carrying concealed weapons...sure it's legal, but they ought to take extra precautions.

Sorry to disappoint you Bob. I have owned several SUVs and large trucks. This Expedition out brakes and out handles all others that I have owned to date. My Expedition also came from the factory with Pirelli tires. These particular tires are highly rated for traction, temperature and wear. Now don’t get me wrong, it’s no sports car but then again I don’t drive it like that. I drive it well within its design limits. How do I know the brakes are massively oversized on my Expedition you ask? Several things… It will go down long mountain grades with several thousand pounds of trailer behind it without any ill effects; general observation and comparison with automotive brakes over many years and the belief that a company that has been building automobiles since the first part of the last century might actually know a thing or two about automotive braking systems.

Poor rollover rating? Very few and I mean very few automobiles have a five star rollover rating. Almost every small sedan has a four-star rollover rating. The Expedition with all wheel drive also has a four star rating. I have the two wheel drive model which causes the rating to barely slip to a three star rating. I don’t worry about that too much though as rollovers are reasonably low with regard to the types of accidents that occur. Additionally, my Expedition has a plethora of safety technologies to minimize the chance for rollover. The statistic that I have is that the electronic stability control (ESC) reduces the chance of rollover 70 to 80%. This combined with the roll stability control (RSC), traction control etc. minimizes the chances of rollover in my Expedition. The interesting thing about the roll stability control on the Expedition is that it uses, among other things, a gyroscopic sensor, which monitors the roll and yaw of the vehicle approximately 100 times every second and can cut engine power while simultaneously engaging brakes either individually or collectively to maintain the vehicle’s stability.

Yes Bob, certain types of avoidance accidents, like running into the back of someone, might be avoided by being able to quickly steer around them but staying a safe distance from them would accomplish the same thing. The accidents I worry about are not minor fender benders so much as someone running a red light doing 45 mph and hitting me in the drivers side or a head on collision. As I previously stated, if a 6,000 pound truck/SUV has a head on collision with a smaller vehicle weighing half as much, the people in the smaller car are eight times more likely to die than the person in the larger of the two vehicles. Another advantage of riding higher in my Expedition is that if I am hit in the driver side door by a Honda Civic or something similar, the main impact will be at the level of my feet. Consequently, if my Expedition impacts the driver’s side door of a Civic, the strongest part of my vehicle (the frame) will impact the Civic driver predominantly in the area where his vital organs are located. Personally speaking, I hope I never have to find out how safe my Expedition is and I pray to God that neither of us ends up seriously hurt in an auto accident.

Bob it seems that you are worried about being hit by a big vehicle. Why don’t you just buy something of reasonable size and safety? Additionally Bob, if you want to come back at me, please come up with something substantive and not just some meaningless, factless, emotional filled dribble. I’m getting tired of schooling you and unless you can come up with something better than you have in your last three posts, I’ll probably just ignore you.

You know all this talk about saving the world from killer SUVs is putting me in the mood to run out to my front yard, throw my arms around the nearest tree and give it a big ol’ hug.

"Expedition out brakes and out handles all others that I have owned to date." Wow...Then your previous vehicles must have really sucked in these areas.

"How do I know the brakes are massively oversized on my Expedition you ask? Several things It will go down long mountain grades with several thousand pounds of trailer behind it without any ill effects;" If there were ill effects simply from this then it shouldn't even be on the road...this is just an example of the brakes doing their basic job, not an example of them being massively oversized.

"Additionally Bob, if you want to come back at me, please come up with something substantive and not just some meaningless, factless, emotional filled dribble." That may be your opinion, but there's no denying the fact, like you pointed out, that a person driving a huge SUV is 8 times more likely to kill somone in a smaller vehicle, so the less huge SUVs out on the roads the better for the millions of people who cannot afford to own, maintain and put gas in a $50,000 huge SUV.

You ask why I don't buy something bigger, but of course you're missing the point again on the needs of society over individual needs. When you're sitting up there in your huge SUV that you don't need, why not try for a few seconds to think about the other drivers on the road and think about their safety.

"As I previously stated, if a 6,000 pound truck/SUV has a head on collision with a smaller vehicle weighing half as much, the people in the smaller car are eight times more likely to die than the person in the larger of the two vehicles." This fact alone is reason why I think it's not responsible driving a 6,000 pound truck/SUV if you don't need to. The less of these types of vehicles on the road the less deaths there will be because the less likelyhood you'll have these types of collisions.

The bottom line is that to me at least, the safety of the millions of people driving small and mediums sized vehicles is more important then the safety of the few individual wanting to drive these huge SUVs. You can respond if you want, but every fact you provide just proves my point more.

Got to agree with Motorhead15 on this. Seen to many small cars flattened by SUV's and the car always comes out the loser. As for me, I want my family and myself the safest I can be in a big vehicle. Hate paying for more gas... but worth it for safety.

I'm not denying the fact that in a contest between a 6000lb vehicle and one half its size that the 6000lb vehicle will come out ahead, I'm just saying that reducing the number of 6000lb vehicles out there on the road will make it safer for the vast majority of people not driving 6000lb vehicles.

Something sized liked a Highlander, Acadia, Pilot, etc will provide plenty of safety and the up-high feeling but won't be so damaging to smaller cars as the really huge SUVs. I'm not saying that owners of huge SUVs have to buy Smart cars, but just something more reasonble to their needs to provide themselves and others safety.

Again...my opinion is that safety goes beyond my own safety. What about your friends and family? Are they all driving 6000lb SUVs all the time? If not then think about how much safer THEY would be if there were less 6000lb SUVs on the road...unless you're rich enough to buy all your friends and families 6000lb SUVs!

"For the safety of one's family one should also seek to free our economy from the balance of payments deficit from our consumption of imported oil. "

Exactly...the problem with most Americans is that they are too short sighted and don't look much beyond the mirror when making decisions. Like little kids...they want everything right now and who cares about anyone else here now or in the future.